The present invention relates to a structure for transporting, installing and dismantling a deck of an off-shore exploitation rig.
The invention also relates to methods for transporting, installing and dismantling a deck of a sea platform by means of such a structure.
For oil development, it is known how to place above an oil deposit, a fixed or floating platform which comprises a deck notably bearing exploitation equipment and living quarters.
The deck is mounted on a supporting structure consisting of at least one supporting column supported on the sea bed or anchored on the latter.
In order to install the deck on this supporting structure, it is known how to use lifting cranes mounted on barges and which allow transfer of the deck from the transport ship onto this structure.
This method which is the most widespread up to now has limitations.
Indeed, the first of these limitations is the capacity of the lifting cranes which may impose that the deck be made in several elements which significantly increases the manufacturing cost of this deck and the cost for installing and dismantling the deck of the platform.
The second limitation lies in the fact that this method imposes the availability of a relatively long favorable time window in order to be able to perform the different transfer operations at sea under good conditions.
Thus, this method may be difficult to apply without considerably increasing the cost in areas where the time windows are relatively short, such as for example in the North Sea.
A second method consists of installing the deck of the platform in a single block on the supporting structure by having it float above the latter.
Next, the deck is positioned on this structure by a ballasting-deballasting system.
In the case of such a ballasting-deballasting system, the deck of the platform is supported by a floating support notably formed by two barges.
One of the important operations lies in the installation of the deck of the platform on these two transport barges.
Indeed, the deck of the platform has to be manufactured and assembled on a same manufacturing site and then transferred from the manufacturing site onto a transfer barge by known means. This transfer barge supporting the deck is then towed towards another site in order to transfer the deck onto two transport barges there.
The transfer barge supporting the deck is brought closer to one of the transport barges which includes means for fixedly supporting the deck. The deck of a platform includes on its sides, complementary means for engaging with the fixed supporting means of the first transport barge.
These complementary engagement means are engaged on the fixed supporting means by moving the transfer barge towards the first transport barge.
Next, the second transport barge which also includes similar fixed supporting means is moved towards the opposite side of the deck of the platform so as to engage the complementary engagement means on the fixed supporting means of the second transport barge.
When both transport barges are engaged under the deck, the transfer barge is then ballasted in order to transfer the whole load of the deck onto the two transport barges.
The transfer barge is then withdrawn and both transport barges supporting the deck are towed up to the exploitation site. The deck is then transferred onto the supporting structure which, in the case of a floating structure is then deballasted in order to transfer the deck onto this supporting structure. Both transport barges may then be reused for another transport.
The installation of the deck on the supporting structure is carried out in the open sea and sea conditions are not always perfect and a residual swell is permanently present.
Consequently, one of the problems posed by this installation method lies in the fact that the elements of the barges supporting the deck will hit this deck under the effect of the swell driving these elements into a to-and-fro motion.
Moreover, in U.S. Pat. No. 6,374,764, a third method is known for installing a deck on a supporting structure which consists of fitting out this deck, on two opposite sides, with legs supporting a barge. Each leg secured to the deck is associated with a driving mechanism with which said deck may be lifted when the barges are floating in order to displace it above the supporting structure.
But, the main drawback of this method lies in the fact that the deck equipped with legs and barges is made more heavy which increases the mass which the supporting structure has to support.
The object of the invention is to propose a structure for transporting a deck of an off-shore platform which avoids these drawbacks and which is designed in order to simplify and reduce the time for installing and dismantling this deck.
For this purpose, the object of the invention is a structure for transporting, installing and dismantling a deck of an off-shore platform, for installing or dismantling this deck on at least one supporting column, characterized in that it comprises two transport barges and means for supporting and lifting the deck, independent of said deck on the one hand and independent of said barges on the other hand and capable of being borne by these barges in order to support said deck between said barges.
The transport structure according to the invention may include one or more of the following features:                the supporting and lifting means are formed with substantially vertical columns each including means for temporary attachment onto the corresponding barge, said attachment means allowing angular displacement of the corresponding column on either side of the longitudinal axis of the barge,        the attachment means form a temporary supporting area of each column on the barge;        each column is provided with a shuttle which may be displaced by mechanical driving means on the corresponding column and including means for temporary connection with the deck,        the temporary attachment means of each column are formed with a half axle provided at the base of the column and extending parallel to the longitudinal axis of the corresponding barge and with a housing having a shape mating said half-axle and made on said barge,        each column is associated with assemblies of legs for maintaining it in a substantially vertical position, said legs being secured to the barge and providing with the corresponding column play for angular displacement of said column,        the mechanical driving means of each shuttle comprise at least two opposite assemblies, borne by the corresponding shuttle and each formed by a pinion driven into rotation and capable of cooperating with a rack borne by the corresponding column, and        means for temporary connection of the shuttles with the deck comprise complementary fitting members borne by said shuttles and said deck and members for locking the deck on the shuttles.        
The object of the invention is also a method for transporting and installing a deck of an off-shore platform onto at least one supporting column by means of a structure as defined above, characterized in that it includes the following steps:
a) the deck is transferred from an assembly quay onto a transfer barge,
b) the transfer barge bearing the deck is displaced and this transfer barge is placed between two barges of the transport structure,
c) the shuttles are displaced upwards on the columns in order to secure these shuttles with the deck by the temporary connection means,
d) the deck is lifted by the shuttles in order to move it away from the transfer barge,
e) the columns are wedged on the assemblies of supporting legs and the transfer barge is withdrawn,
f) the shuttles bearing the deck are lowered and the deck is attached onto the barges,
g) the barges are displaced in order to bring the deck up to the exploitation site including at least said column,
h) the deck is detached from the barges,
i) the deck is lifted by the shuttles,
j) the barges are displaced in order to place the deck above at least said supporting column,
k) the shuttles are lowered,
l) the deck is laid on at least said supporting column,
m) the deck is detached from the shuttles,
n) the shuttles are lowered, and
o) the transport barges are withdrawn.
An object of the invention is also a method for dismantling and transporting a deck of an off-shore platform by means of a structure as defined above, characterized in that it includes the following steps:
a) the barges fitted out with columns beforehand each bearing one shuttle is placed on either side of said at least supporting column,
b) the shuttles are displaced upwards on the columns in order to secure the shuttles with the deck through the temporary connection means,
c) the deck is detached from said at least supporting column,
d) the deck is lifted by the shuttles in order to move it away from said at least supporting column
e) the barges bearing the deck are displaced,
f) the shuttles bearing the deck are lowered and the deck is attached onto the barges,
g) the barges are displaced in order to bring the deck up to a transfer barge,
h) the deck is detached from the barges,
i) the deck is lifted by the shuttles,
j) the transfer barge is placed between the barges and above the deck,
k) the shuttles are lowered in order to lay the deck on the transfer barge,
l) the deck is attached onto the transfer barge,
m) the deck is detached from the shuttles,
n) the shuttles are lowered,
o) the barges are withdrawn, and
p) the deck is transported by the transfer barge up to a dismantling site.
The invention will be better understood upon reading the description which follows, only given as an example and made with reference to the appended drawings, wherein:
With the purpose of facilitating the understanding of the drawings, the scales between the different elements making up the structure are not always observed.